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Laser metal deposition of copper on diverse metals using green laser sources
摘要： Green laser sources are advantageous in the processing of copper due to the increase of absorptivity compared with more commonly available infrared lasers. Laser metal deposition of copper with a green laser onto various substrate metals namely copper, aluminium, steel and titanium alloy was carried out and observed through high-speed imaging. The effects of process parameters such as laser power, cladding speed and powder feed rate, and material attributes such as absorptivity, surface conditions and thermal conductivity are tied together to explain the size and geometry of the melt pool as well as the fraction of the power used for melting material. The copper substrate has the smallest melt pool with a high angle, followed by aluminium, steel and titanium alloy. The incorporation times for powder grains in the melt pools vary based on the substrate materials. Its dependency on material properties, including surface tension forces, melting temperatures and material density, is discussed. Oxide skins present on melt pools can affect powder incorporation, most significantly on the aluminium substrate. The lower limits of the fraction of power irradiated on the surface used purely for melting were calculated to be 0.73%, 2.94%, 5.95% and 9.78% for the copper, aluminium, steel and titanium alloy substrates, respectively, showing a strong dependence on thermal conductivity of the substrate material. For a copper wall built, the fraction was 2.66%, much higher than a single clad on a copper substrate, due to reduced workpiece heating. The results of this paper can be transferred to other metals with low absorptivity such as gold.
关键词： Multi-material,DED,High-speed imaging,LMD,Copper,Green 515-nm laser,Laser metal deposition,Powder grain incorporation,Additive manufacturing,Directed energy deposition,Absorptivity
更新于2025-09-19 17:13:59
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Numerical modelling of heat transfer, mass transport and microstructure formation in a high deposition rate laser directed energy deposition process
摘要： In laser directed energy deposition (L-DED) processes, by applying a converged powder stream, relatively high laser power and larger laser spot, the powder utilisation efficiency and processing speed can be increased. There is, however, lack of mathematical models for L-DED. In this paper, a three-dimensional numerical model is established to study the mass transport and heat transfer in the melt pools in high deposition rate (HDR) L-DED of 316L stainless steel. The Volume of Fluid (VOF) method is employed to track the melt pool free surfaces, and enthalpy-porosity method is used to model the solid-liquid phase change. A discrete powder source model is developed by considering the non-uniform powder feed rate distribution. Results show that this model can well predict the deposited track dimensions (width, height and dilution depth). Different from conventional L-DED processes, the impact of higher mass addition on the melt pool fluid flow and temperature distribution is significant. In the regions where filler powder is injected, a downward mass flow is observed, and the temperature is slightly reduced. With the extracted temperature distribution and geometry at the solidification front, the solidification conditions are also calculated, as well as the primary dendrite arm spacing (PDAS) of the solidified tracks. Due to the high laser energy input, the temperature gradient is lower, and coarser microstructures are formed compared with conventional L-DED. The simulated results are in good agreement with experimental results.
关键词： Heat transfer,High deposition rate laser directed energy deposition,Mass transport,Primary dendrite arm spacing
更新于2025-09-19 17:13:59
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Beyond the Toolpath: Site-Specific Melt Pool Size Control Enables Printing of Extra-Toolpath Geometry in Laser Wire-Based Directed Energy Deposition
摘要： A variety of techniques have been utilized in metal additive manufacturing (AM) for melt pool size management, including modeling and feed-forward approaches. In a few cases, closed-loop control has been demonstrated. In this research, closed-loop melt pool size control for large-scale, laser wire-based directed energy deposition is demonstrated with a novel modification, i.e., site-specific changes to the controller setpoint were commanded at trigger points, the locations of which were generated by the projection of a secondary geometry onto the primary three-dimensional (3D) printed component geometry. The present work shows that, through this technique, it is possible to print a specific geometry that occurs beyond the actual toolpath of the print head. This is denoted as extra-toolpath geometry and is fundamentally different from other methods of generating component features in metal AM. A proof-of-principle experiment is presented in which a complex oak leaf geometry was embossed on an otherwise ordinary double-bead wall made from Ti-6Al-4V. The process is introduced and characterized primarily from a controls perspective with reports on the performance of the control system, the melt pool size response, and the resulting geometry. The implications of this capability, which extend beyond localized control of bead geometry to the potential mitigations of defects and functional grading of component properties, are discussed.
关键词： closed-loop control,lasers,metal,directed energy deposition,additive manufacturing,3D printing,titanium,site-specific,melt pool size
更新于2025-09-19 17:13:59
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Nonlinear energy deposition of filamentation with femtosecond Airy laser beams in water
摘要： The nonlinear propagation of femtosecond Airy laser ?laments in water is numerically investigated in this paper. We mainly consider the in?uences of con?nement parameter, pulse duration and beam waist on the deposited energy of ?laments. The values of con?nement parameter are found to have a signi?cant impact on the temporal and spatial dynamics of the pulse. The characteristics of energy deposition also di?er widely for Airy beams with di?erent con?nement parameters. The less the con?nement parameter, the more energy deposited by ?lamentation. However, the relative deposited energy evolves relatively small changes under di?erent con?nement parameters. We also found the longer pulse duration and longer beam waist are bene?cial to the total deposited energy increase.
关键词： self-focusing,Airy beams,energy deposition,Ultrafast nonlinear optics
更新于2025-09-19 17:13:59
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In-Process Laser Re-Melting of Thin Walled Parts to Improve Surface Quality after Laser Metal Deposition
摘要： Laser metal deposition (LMD) is an additive manufacturing process highly adaptable to medium to large sized components with bulky structures as well as thin walls. Low surface quality of as-deposited LMD manufactured components with average roughness values (Ra) around 15-20μm is one of the main drawbacks that prevent the use of the part without the implementation of costly and time-consuming post-processes. In this work laser re-melting is applied right after LMD process with the use of the same equipment used for the deposition to treat AISI 316L thin walled parts. The surface quality improvement is assessed through the measurement of both areal surface roughness Sa(0.8mm) and waviness Wa(0.8mm) parameters. Moreover, roughness power spectrum is used to point out the presence of principal periodical components both in the as-deposited and in the re-melted surfaces. Then, the transfer function is calculated to better understand the effects of laser re-melting on the topography evolution, measuring the changes of individual components contributing to the surface roughness such as the layering technique and the presence of sintered particles. Experiments showed that while low energy density inputs are not capable to properly modify the additive surface topography, excessive energy inputs impose a strong periodical component with wavelength equal to the laser scan spacing and directionality determined by the used strategy. When a proper amount of energy density input is used, laser re-melting is capable to generate smooth isotropic topographies without visible periodical surface structures.
关键词： laser metal deposition,direct energy deposition,Additive manufacturing,post-processing,surface roughness,laser re-melting
更新于2025-09-16 10:30:52
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A Hybrid Modeling of the Physics-Driven Evolution of Material Addition and Track Generation in Laser Powder Directed Energy Deposition
摘要： Directed Energy Deposition (DED) is one of the most promising additive manufacturing technologies for the production of large metal components and because of the possibility it offers of adding material to an existing part. Nevertheless, DED is considered premature for industrial production, because the identification of the process parameters may be a very complex task. An original hybrid analytic-numerical model, related to the physics of laser powder DED, is presented in this work in order to evaluate easily and quickly the effects of different sets of process parameters on track deposition outcomes. In the proposed model, the volume of the deposited material is modeled as a function of process parameters using a synergistic interaction between regression-based analytic models and a novel element activation strategy. The model is implemented in a Finite Element (FE) software, and the forecasting capability is assessed by comparing the numerical results with experimental data from the literature. The predicted results show a reasonable correlation with the experimental dimensions of the melt pool and demonstrate that the proposed model may be used for prediction purposes, if a specific set of process parameters that guarantees adequate adhesion of the deposited track to the substrate is introduced.
关键词： laser powder deposition,finite element model,thermal analysis,directed energy deposition,additive manufacturing
更新于2025-09-16 10:30:52
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The influence of laser engineered net shaping (LENSa?￠) technological parameters on the laser deposition efficiency and properties of H13 (AISI) steel
摘要： A successful attempt at laser cladding of H13 (AISI) hot work tool steel by the laser engineered net shaping technique is presented. Technological parameters, such as laser spot diameter, powder flow rate, and deposition velocity, were changed during the experiment. The influences of the different technological parameters on the efficiency of the cladding, geometry of the clads and properties of the deposited material were investigated. As a result, 75 different samples were deposited. The efficiency of the cladding varies significantly within the chosen range of parameters and is as low as several percentage points. The chosen parameters also appear to affect the shape of the clad, size of the heat-affected zone, microstructure and hardness of the steel, which ranged from 500 to 800 HV after deposition. The proper choice of parameters led to the desired surface hardness of the deposited material, and a heat treatment of the final product may not be necessary.
关键词： Clads geometry,Direct energy deposition,Deposition efficiency,Laser cladding,Microstructure,H13 tool steel,Microhardness,LENS?
更新于2025-09-16 10:30:52
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Application of laser energy deposition to improve performance for high speed intakes
摘要： Research interest has been growing in recent years in supersonic transport, particularly supersonic propulsion systems. A key component of a commonly studied propulsion system, ramjets, is the air intake. For supersonic propulsion systems a major factor in the overall efficiency is the intake pressure recovery. This refers to the ratio of the average total pressure after the intake to that of the freestream. One phenomenon that can have a large effect on this performance index is flow separation at the inlet. The aim of this work is to examine how pulsed laser energy deposition can be used to improve pressure recovery performance by reducing flow separation at the inlet. This research examines the effects of pulsed laser energy deposition upstream of an intake with an axisymmetric centrebody in a Mach 1.92 indraft wind tunnel. Laser frequency was varied between 1 and 60 kHz with an energy per pulse of 5.6 mJ. Schlieren photography was used to examine the fundamental fluid dynamics while total and static pressure downstream of the intake diffuser were measured to examine the resulting effect on the performance. Schlieren imaging shows that the interaction between the laser generated thermal bubble and the leading edge shock produced by the centrebody results in a significant reduction in separation along the intake cone. Analysis of the schlieren results and the pressure results in tandem illustrate that the average separation location along the length of the centrebody directly correlates to the pressure recovery observed in the intake. At the optimal laser frequency, found for this Mach number to be 10 kHz, the pressure recovery is found to increase by up to 4.7%. When the laser power added to the system is considered, this results in an overall increase in propulsive power of 2.47%.
关键词： Intakes,Supersonic,Flow dynamics,Flow separation,Laser energy deposition
更新于2025-09-16 10:30:52
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Propagation of circularly polarized laser in strongly magnetized over-dense collisional plasma
摘要： Permittivity of a circularly polarized (CP) laser in magnetized collisional plasma is obtained in simpli?ed form. The propagation of a CP laser in magnetized homogeneous over-dense collisional plasma was investigated, and characteristics such as attenuation length, speci?c energy deposition and blue shift are obtained. Potential applications in ?elds such as inertial con?ned fusion are discussed.
关键词： energy deposition,collisional plasma,permittivity,inertial con?ned fusion,attenuation length,blue shift,circularly polarized laser,magnetized plasma
更新于2025-09-16 10:30:52
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Influence of Process Parameters and Deposition Strategy on Laser Metal Deposition of 316L Powder
摘要： In blown powder additive manufacturing technologies the geometrical stability of the built parts is more complex with respect to more conventional powder bed processes. Because of this reason, in order to select the most suitable building parameters, it is important to investigate the shape and the properties of the single metal bead formation and the effect that a scan track has on the nearby ones. In the present study, a methodology to identify an appropriate laser metal deposition process window was introduced, and the effect of the building parameters on the geometry of circular steel samples was investigated. The effect of the scanning strategy on the deposited part was also investigated. This work draws the attention to the importance of the obtainment of the most suitable melt pool shape, demonstrating that the laser power and the scanning strategy have a strong influence not only on the shape but also on the mechanical properties of the final component.
关键词： steel,additive manufacturing,melt pool,overlap,scanning strategy,directed energy deposition,AISI 316L
更新于2025-09-16 10:30:52